1. Field of the Invention
The present invention relates to an electron-emitting device provided on the surface of a substrate, and an electron-beam generator equipped with the device.
2. Related Background Art
Hitherto known as a device achievable of emitting electrons with use of a simple structure is the cold cathode device published by M. I. Elinson et al (Radio Eng. Electron. Phys., Vol. 10, pp. 1290-1296, 1965.
This utilizes the phenomenon in which electron emission is caused by flowing an electric current to a thin film formed with a small area on a insulating substrate and in parallel to the surface of the film, and is generally called the surface conduction type electron emission device.
This surface conduction type electron emission device that has been reported includes those employing a SnO.sub.2 (Sb) thin film developed by Elinson et al named in the above, those comprising an Au film (G. Dittmer, "Thin Solid Films", Vol. 9, p. 317, 1972), those comprising an ITO thin film (M. Hartwell and C. G. Fonstad, "IEEE Trans. ED Conf.", p. 519, 1975), and those comprising a carbon thin film [Hisa Araki et al., "SHINKU (Vacuum)", Vol. 26, No. 1, p.22, 1983].
These surface conduction type electron emission devices have the advantages that;
(1) they can achieve a high electron-emission efficiency; PA0 (2) they are simple in construction and hence can be manufactured with ease; PA0 (3) a number of devices can be formed by arranging them on the same substrate; PA0 (4) they can attain a high speed of response; and so forth
and can henceforth promise to be widely applied.
However, in the conventional electron-emitting devices, the insulating substrate on which the electron-emitting device is formed has an unstable potential, causing the problem that the orbits of the electrons emitted become unsteady.
FIG. 1 shows an example to explain this problem, and partially illustrates a display unit in which a conventional surface conductance electron-emitting device is applied. The numeral 1 denotes an insulating substrate made of, for example, glass; and 2 to 5, component elements of the surface conduction type electron emission device, where the numeral 2 denotes a thin film made of a metal or a metal oxide, or carbon, etc., and an electron-emitting area 5 is formed at part thereof by a conventionally known forming treatment. The numerals 3 and 4 denote electrodes provided to apply a voltage to the thin film 2, which are used setting the electrode 3 serving as the positive electrode, and the electrode 4, as the negative electrode. The numeral 6 denotes a glass sheet, on the inner surface of which a phosphor target 8 is provided interposing a transparent electrode 7.
In this unit, the phosphor target 8 can be made to emit light by applying an accelerating voltage of, for example, 10 kV to the transparent electrode 7 and simultaneously applying a given voltage between the electrodes 3 and 4 of the surface conduction type electron emission device, thereby effecting emission of electron beams.
In the case of this unit, however, the orbits of the electron beams is not necessarily steady to cause a change of the shapes of luminescent spots on the phosphor target, resulting in a lowering of the quality level of a displayed image to bring about a serious difficulty.
This is because the substrate 1 in which the surface conduction type electron emission device is provided has so an unstable potential that the electron beams therefrom are adversely influenced. In particular, the potential at the peripheral area of the electron-emitting area 5, as shown by a shaded portion in the figure, greatly influence the orbits of electron beams. Such a difficulty has been caused even in other units having a different construction from that of FIG. 1, for example, a display unit comprising an electrode additionally provided between the electron-emitting device and the transparent electrode 7, for the purpose of the draw-out, strength modulation or deflection of electron beams, or an electron beam drawing unit equipped with an image forming material other than the phosphor as the target of electron beams.